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Chapter 38: Digestive System 2 Major Patterns of Digestion A. Intracellular • Digestion occurs w/in cells • Lysosomes release enzymes into food vacuoles, breaks down occurs w/in these vacuoles - (lysis- splitting, some- body) • Ex: a. Sponges, unicellular organisms b. Plants starch converts to simple sugars (in every cell) c. Cnidaria (hydra) partly intra/ extracellular d. Humans some food in small intestine (SI) undergoes final breakdown w/in cells (proteins, lipids) - BUT digestion largely EXTRACELLULAR! B. Extracellular • Digestion outside the cell, usually w/in a cavity lined by these cells • Ex: a.Molds, mushroom (other fungi) b. Plants (Venus fly trap, pitcher plant) insectivorous - Autotrophs, but have adaptations to trap insects- source of nitrogen c. Humans most food digested w/in digestive cavity (aka alimentary canal) Cont. Extracellular d. Worms (Platyhelminthes) carnivorous - Incomplete digestive tract- 1 opening that serves as mouth/ anus – Food partially digested by pharynx (food tube) outside the body; digestion completed w/in body e. Starfish pushes out stomach; digest clam w/in shell f. Earthworm complete digestive system- 2 openings – Mouth pharynx crop gizzard intestine anus – Food & soil enter mouth, pass through digestive system – Wastes called “castings” sold commercially as “super stuff”/ fertilizer enriches soil C. Hydrolysis • Chemical process in which larger molecules are broken down into smaller soluble subunits by addition of water. (+H2O) 1. Proteins -------------------- (+H2O) (hydrolysis) -----------------► Amino Acids ◄-------------------- (- H2O) (dehydration synthesis) --2. Polysaccharides --------- (+ H2O) ----------------► Monosaccharides (Starches)◄---------------- (- H2O) ------------------- Simple sugars 3. Lipids ------------------------ (+ H2O) ---------------► 3 Fatty acids & glycerol ◄---------------------- (- H2O) ---------------4. Nucleic Acids -------------- (+H2O) ----------------► Nucleotides (Cell nuclei)◄-------------- (- H2O) ------------------ (DNA- A, C, G, T) (RNA- A, C, G, U) Digestion- 2 Major Phases A. Physical Phase: change in size or movement of food molecules • Chewing- mastication • Swallowing- deglutition • Peristalsis- wave-like muscle contractions through alimentary canal; moves food from one area to another • Segmentation- (small intestine) mixes enzymes and food • Emulsification- (bile secreted by liver into small intestine); physical breakdown of lipids from larger lipids to smaller sized lipidsfacilitates the chemical breakdown of lipids by pancreatic lipase B. Chemical Phase: carried out by hydrolases- enzymes which bring about hydrolysis 1. Protein + H2O ------------------------ Amino acids (soluble- can be absorbed into (proteases) cells) 2. Lipids + H2O --------------------- 3 Fatty acids & glycerol (soluble) (lipases) 3. Carbohydrates + H2O --------------- Disaccharides (maltose, sucrose, lactose) (amylases) 4. Disaccharides + H2O ---------------- Monosaccharides (simple sugars- soluble) (disaccharases) a. Sucrose- sucrase + H2O ------ glucose & fructose b. Maltose- maltase + H2O ------- glucose & glucose c. Lactose- lactase + H2O -------- glucose & galactase 5. Nucleic Acids + H2O ---------------- Nucleotides (ribose/ deoxyribose, + (Pancreas- deoxyribonuclease) nitrogen base + phosphate) (Pancrease- ribonuclease) (for DNA- A,C, G, T// for RNA- A, C, G, U) Human Digestion A. Essential Nutrients (6 types) Energy foods Non-energy foods 1. Amino acids (from protein) 1. Minerals 2. CHO (starches & sugars) 2. Vitamins (All 3 regulates body fxns) 3. Lipids (fats & oil) 3. Water • Water makes most of cell volume/ main solvent •70-90% depending on cell type B. Anatomy of Human Digestive Tract 1. Alimentary Canal • • Mouth esophagus stomach small intestine (duodenum, jujenum, ileum) large intestine (colon) rectum anus These organs make DIRECT contact w/ food molecules 2. Accessory Organs • DO NOT make contact with food/ secrete into alimentary canal a. Salivary glands (3 pairs)- parotid, submaxillary, sublingual b. Pancreas c. Liver d. Gallbladder C. Small Intestine- Absorption of Digested Nutrients • • • • Approx 16 ft long in adults Surface area greatly increased by villi to allow for maximum absorption of soluble food molecules into blood & lacteals (lymph vessels) Epithelial layer cells absorb soluble nutrients Each villus contains capillaries & a lymph vessel Cross-Section of S.I. Capillaries absorb: Lymph vessels (lacteal) absorb: 1. Monosaccharides 1. Fatty acids 2. Amino acids 2. Glycerol 3. Some glycerol 4. Minerals 5. Vitamins 6. Water *Cap 1-6 are carried to liver by portal vein via hepatic portal system D. Hepatic Portal System 1. Portal System – Venous system which transports blood through a specific organ before it is returned to the heart 2. Hepatic Portal System – Venous system carrying digested foods from the digestive system to the LIVER – Main vein is the portal vein which enters the liver 3. Liver -- Maintains the concentrations of organic nutrients in the blood by converting 1 type of organic nutrients into others • Examples: (Deamination) ----------------------- CHO a. Amino Acids (AA) -------------------- - NH2 ----------------------- Lipids (Amino group) ------------------- Urea excreted by kidney (Amination) b. CHO --------------------------------- + NH2 ------------------------ Nonessential AA Lipids c. CHO --------------------------------- Lipids AA (- NH2) Cont. Hepatic Portal System 4. Essential Amino Acids (8) -Can’t be synthesized by the body; acquire through diet 5. Non-essential Amino Acids (12) - Can be synthesized by the body Hormones Which Regulate Digestion Organ Hormone Target Effect 1. Stomach (pyloric region) + presence of food Gastrin Stomach mucosa a. Release H+ & Clinto cavity forms HCl b. Release pepsinogen 2. Duodenum (1st 10 in of SI) + presence of food Secretin Pancreas NaHCO3 (baking soda) Pancreozymin (cholecystokinin) Pancreas, liver, & gallbladder * Bile release into *Bile emulsifies lipids * Pancreatic lipase duodenum causes (causes physical hydrolyzes lipids into fatty acids & glycerol relaxation of Spincter breakdown) of Oddi 4 different type of enzymes: a. Amylase b. Lipase c. Proteases d. Nucleases The Digestive Enzymes **know which Section 38-2 macromolecules are broken down in each organ Site Enzyme Role in Digestion Mouth Salivary amylase Breaks down starches into disaccharides Stomach Pepsin Breaks down proteins into large peptides Small intestine (from pancreas) Amylase Continues the breakdown of starch Trypsin Continues the breakdown of protein Lipase Breaks down fat Maltase, sucrase, lactase Breaks down remaining disaccharides into monosaccharides Peptidase Breaks down dipeptides into amino acids. Small intestine